This invention relates to a process for recovering hydrocarbon values from an underground hydrocarbon-bearing formation. More particularly, the invention relates to a process for recovering these hydrocarbons by electrothermal means, wherein the subterranean formation is heated, thus making the hydrocarbon values mobile and recoverable. A broad statement of the complete process includes these steps:
(a) the formation of underground electrodes of enlarged radius, PA1 (b) using the formed electrodes to heat the formation between wells, thus making the hydrocarbon material (bitumen) mobile, and PA1 (c) removal and recovery of the mobile material, such as by a displacing fluid. PA1 (a) placing a heating device in the first borehole, PA1 (b) energizing the device to heat the surrounding formation to a temperature high enough to produce coking of at least a portion of the hydrocarbon-bearing formation, thus forming a coked zone, which, having conductive properties, acts as an electrode, PA1 (c) maintaining the temperature of step (b) for a length of time to obtain a coked zone electrode having an effective radius at least twice that of the borehole, PA1 (d) repeating steps (a-c) in a second borehole, PA1 (e) applying an electromotive potential between the coked zone electrodes of the first and second boreholes, to heat the formation between the boreholes to a temperature at which the hydrocarbon values are mobile, and PA1 (f) recovering hydrocarbon values from one of said boreholes.
The utility of the invention lies in the recovery of hydrocarbons from an underground formation.
Although a majority of petroleum is produced from freely-flowing wells drilled into a subterranean formation, there are many hydrocarbonaceous materials that cannot be produced directly in such a manner--some supplemental operation is required to recover such materials. Secondary and tertiary methods of recovering petroleum are wellknown, such as water-flooding or steam-flooding. If the hydrocarbon values in the underground formation are too viscous or are otherwise retained in the formation, one method of reducing the viscosity or liberating the hydrocarbon values is by the application of heat to the underground formation. Heat energy can be introduced to the underground formation by means of a heated liquid or gas or by the combustion of a portion of the underground hydrocarbon values. Another method of introducing heat energy is by the use of electrical energy in the subterranean formation, resulting in resistance heating.
However, there are problems in heating by electricity. If the temperature in the vicinity of the electrode wellbore is not kept below the vaporization temperature of connate water typically found in the subterranean formation, the removal of this connate water by vaporization effectively hinders the flow of current into the formation, thus limiting the amount of formation heating.
Since the prior art methods of heating a subterranean formation, and thus recovering hydrocarbon values, have not been totally satisfactory, I submit that my invention overcomes the difficulties encountered and offers an improved method of recovering hydrocarbon values from an underground hydrocarbon-bearing formation.